Collapse resistance of tubing

ABSTRACT

A method of increasing the collapse resistance of a tubular comprises locating a tool having at least one, and typically three, bearing members within a tubular. The bearing members are positioned in engagement with a wall of the tubular to apply a radial force to a discrete zone of the wall. This radial force is then applied to further discrete zones of the wall, the level of radial force being selected such that the collapse resistance of the tubular is increased.

FIELD OF THE INVENTION

[0001] This invention relates to improving the collapse resistance oftubing, particularly tubing to be utilised in downhole applications.

BACKGROUND OF THE INVENTION

[0002] Bores drilled to access subsurface hydrocarbon reservoirs arelined with metal tubing to inter alia prevent-collapse of the bore wallsand to provide pressure integrity. The characteristics of thebore-lining tubing utilised to line a bore will be based on a number offactors, one being the collapse or crush-resistance of the tubing. Thisis the ability of the tubing to withstand external radial forces, as mayresult from fluid pressure or from mechanical forces applied by asurrounding rock formation. The collapse resistance of a section oftubing may be estimated by means of calculations, typically following anAmerican Petroleum Institute (API) standard formulation (API Bulletin5C3). Alternatively, a section of tubing with its ends blanked off maybe immersed in hydraulic fluid which is then pressurised until thetubing collapses.

SUMMARY OF THE INVENTION

[0003] It has been found that the collapse resistance of metallic tubingmay be enhanced, in a preferred embodiment, by applying radial forces todiscrete areas or zones of the tubing, most conveniently by passing arotating tool through the tubing, which tool includes at least onebearing member for applying a radially directed force to the tubingwall.

[0004] In other embodiments of the invention, other means of increasingthe strength or hardness of the tubing are utilised, as will bedescribed.

[0005] Preferably, at least an inner portion of the tubular wall issubject to compressive yield or other cold working, which effect mayalso be achieved through other means, for example by hydraulicallyexpanding the tubular within a higher yield strength outer tubular, orwithin a bore in a substantially unexpandable body of material.

[0006] Conveniently, the tool may be a rotary expansion tool, examplesof which are described, for example, in applicant's International PatentApplication Publication No. WO 00\37766, and in the SPE Paper 74548entitled “The Application of Rotary Expansion to Solid ExpandableTubulars”, by Harrall et al. As described in the SPE paper, when such atool is utilised to expand tubing, the tubular material is subjected tostrain hardening processes, whereby the yield and tensile strengthincrease as a function of expansion ratio and the expandable materialcharacteristics. However, the collapse resistance of the expandedtubular is of course less than the original unexpanded tubing, due tothe decrease in tubular wall thickness and the increase in diameter.

[0007] Surprisingly, it has been found that by passing such an energisedrotary expansion tool through a tubular and subjecting the tubular tominimal deformation, which may be apparent as an increase in the lengthof the tubular, a slight increase in external diameter, or creation ofundulations or a wave form on the tubular inner surface, the collapseresistance of the tubing may be increased. The procedure may be carriedout on surface, before a tubular is run into a bore, or may be carriedout downhole, in existing casing or liner. Of course the radial forcesutilised to increase the collapse resistance of the tubing may beachieved using other tool forms and configurations.

[0008] It is believed that the invention will have particular utility inincreasing the collapse resistance of tubulars which have previouslybeen subjected to swage-expansion. As identified in the above-noted SPEpaper, one of the primary concerns with swage-expanded tubulars is thedetrimental effect of expansion on collapse performance. It has beensuggested that the radial orientation of strain hardening incone-expanded tubulars, and a subsequent reduction in yield on reversed,collapse loading (Bauschinger effect), is the most likely explanation.Indeed, testing of swage-expanded tubulars indicates that the collapseresistance of such tubulars may be significantly lower than the API 5C3predictions for given D/t ratios. Thus the invention may be utilisedimmediately following the swage-expansion of a tubular, or may becarried out as a remedial operation, for example where an operator isconcerned that the integrity of a well may be compromised by thepresence of swage-expanded tubulars which may provide poorer collapseperformance than was originally predicted. Similarly, the presentinvention may be utilised in instances in which well conditions have orare expected to change to an extent that the collapse resistance ofexisting casing or liner is deemed inadequate, or where a problemformation is to be isolated and is expected to exert elevated forces orpressures on the tubing: by means of the relatively simple method of thepresent invention, the collapse resistance of the tubing may beincreased in situ. An entire tubing string may be treated, or only aselected part of the tubing may be treated, for example only the part ofa casing intersecting a swelling formation may be treated.

[0009] Even in applications in which an existing tubular has beencemented in a bore the invention may be utilised to increase thecollapse resistance of the tubular.

[0010] Although not wishing to be bound by theory, it is believed thatthe collapse resistance of a tubular can be enhanced by increasing oneor both of the strength and hardness of the inner fibre, that is theinside diameter (ID) or inner portion of the bore wall. Whilst this hasbeen demonstrated by increasing the ID surface strength by strainhardening or cold work, the invention encompasses other means oflocalised surface hardening using metallurgical transformation ordiffusion of elements which promote increased hardness by solidsolution, precipitation or transformation strengthening mechanisms.

[0011] Examples of methods within the scope of the invention include,but are not limited to, cold work by peening or rolling, inductionhardening, nitriding and carburising. In other words, any suitabletechnique for inducing a compressive stress in the inner surface of atubular, in an effort to increase the collapse resistance of thetubular, may be utilized.

[0012] The invention also relates to tubulars which have been subject tothe method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] These and other aspects of the present invention will now bedescribed, by way of example, with reference to the accompanying,drawing, which is a schematic illustration of a tubular having itscollapse resistance increased, in accordance with an embodiment of anaspect of the present invention.

DETAILED DESCRIPTION OF THE DRAWING

[0014] The drawing shows a metallic tubular 10, such as utilised inconventional downhole applications. Located within the tubular is a tool12 similar to the rotary expansion tools as described in WO 00\37766.The tool 12 features a hollow body 14 in which are mounted threeequi-spaced pistons 16, each piston carrying a roller 18 which isrotatable about an axis substantially parallel to the body mainlongitudinal axis 20.

[0015] The tool 12 is mounted on a pipe string through which pressurisedhydraulic fluid is supplied to the tool body 14. This urges thepiston-mounted rollers 18 radially outwardly into contact with the innerwall of the tubular 10. The tool 12 is rotated about its axis 20 andadvanced axially through the tubular 10.

[0016] The rollers 18 impart a radial force upon discrete zones of thetubular's circumference, cold working the zones, and the rotation of thetools 12 about its longitudinal axis 20 applying this radial force withthe resulting cold working to the entire inner circumference of thetubular 10, or at least to a helical path or paths which encompass asubstantial proportion of the tubular wall.

[0017] The degree of force imparted by the rollers 18, which may bevaried during the operation, may be controlled by applying a selectedfluid pressure, and may be selected to provide a small degree ofdiametric expansion to the tubular 10. Alternatively, there may be noappreciable diametric expansion experienced by the tubular 10, thedeformation of at least the inner surface of the tubular beingaccommodated by creation of undulations in the inner wall surface or byan increase in the length of the tubular. Indeed, in many downholeapplications there will be no opportunity for diametric expansion, forexample if the tubular has been cemented in the bore.

[0018] In some cases, in an effort to accurately control the degree(amount) of radial force imparted to the inner surface of the tubular 10by the rollers 18, one or more sensors may be utilized in conjunctionwith the tool 12. For example, one or more sensors may be utilized todirectly measure the amount of radial force imparted by the rollers 18(e.g., one or more strain gauges operatively coupled with the rollers 18or pistons 16), to measure the fluid pressure applied to the inner body14 of the tool 12 (which may be proportional to the radial forceimparted by the rollers 18), or to measure an increase in diameter ofthe tubular 10. The radial force imparted on the tubular may becontrolled by modulating the fluid pressure applied at the surface, inresponse to any combination of these measured parameters.

[0019] Any suitable arrangement of any suitable type sensors may beutilized to measure such parameters. For example, fiber optic sensors,such as fiber optic sensors which utilize strain-sensitive Bragggratings formed in a core of one or more optical fibers may be utilized.The use of such fiber optic sensors is described in detail incommonly-owned U.S. Pat. No. 5,892,860, entitled “Multi-Parameter FiberOptic Sensor For Use In Harsh Environments”, issued Apr. 6, 1999 andincorporated herein by reference.

[0020] The Bragg gratings may be subjected to strain due to one or moremeasured parameter (e.g., the radial force, fluid pressure or change inouter diameter of the tubular 10). For example, in applications wherethe outer diameter of the tubing 10 is increased, a change in the outerdiameter may be measured with an interferometer formed by two Bragggratings separated by a length of fiber L wrapped around an exterior ofthe tubular 10. Changes in the outer diameter of the tubing 10 may bedetected by monitoring changes in the length L, detected byinterrogating the interferometer. For example, the length L may bedetermined by the number of wraps of the fiber N around the tubular 10,having an outer diameter OD (e.g., L=N×PI×OD).

[0021] Further, utilizing well known multiplexing techniques, such astime division multiplexing (TDM) or wavelength division multiplexing(WDM), different arrays of fiber optic sensors deployed on a commonfiber may be distributed along one or more tubulars 10, for example, tomonitor the radial stress induced at one or more discrete zonesstrengthened by radial stress.

EXAMPLE

[0022] In order to demonstrate the benefit in collapse resistanceobtained using the rotary expansion method as described above, collapsetests on the same material expanded to the same ratio by cone swageexpansion and rotary expansion were conducted.

[0023] Material

[0024] The expanded material was a proprietary cold-finished normalisedaluminium-killed steel designated VM42. The dimensions were 5 ½″ 17#OCTG, i.e. 139.7 mm OD×7.72 mm WT. The rotary expanded material wasidentified as “heat 345640”. In the absence of identifiable heat numberson the cone-expanded specimen, chemical analysis, metallographicexamination and mechanical testing were performed to demonstrate thatequivalent materials were tested. In addition to this, a lowyield-strength quenched & tempered (Q&T) material of the same dimensionswas expanded and collapse tested. Analysis by Optical EmissionSpectrometry. C Si Mn S P Ni Cr Mo Nb Cu Al Ti Nominal VM42 0.15 0.210.94 — — 0.04 0.10 0.01 — 0.07 — — Cone Expanded 0.15 0.20 0.93 0.0040.014 0.03 0.11 — — 0.02 0.034 — VM42 Rotary 0.14 0.24 0.98 0.002 0.013— — — — — 0.029 — Expanded VM42 Rotary 0.11 0.36 1.27 0.002 0.017 0.360.11 0.01 0.022 0.23 0.049 0.02 Expanded Q&T

[0025] The pre-expansion longitudinal and transverse tensile propertiesare shown below. Longitudinal testing was conducted in accordance withBS EN 10002 Pt 1:2001. VM42 Q&T Material Ultimate Tensile Stress MPa469-481 538 Ksi 68.0-69.8 78.0 0.2% Offset Proof Stress MPa 344-357 442Ksi 49.9-51.8 64.1 Elongation % 37-41 29 Cross Sectional Area mm² —94.07 Gauge Length mm 50.8 50

[0026] Metallographic specimens were prepared from the expanded cone androtary expanded VM42 material and also the Q&T steel. The VM42 materialpossessed a banded ferrite-pearlite microstructure consistent with anormalised low carbon steel. The Q&T material exhibited a microstructurecomprising fine, tempered martensite.

[0027] Expansion Test

[0028] Data on the cone-expansion was not available, however thedimensions were consistent with an approximate 139 mm diameter cone. TheOD was 154 mm with an average wall thickness of 7.29 mm, giving an ODexpansion ratio of 10.2%.

[0029] The rotary expansion was conducted using 4.75″ compliant toolwith a single plane of 20° rollers. The expansion was conducted at4′/min and 50 rpm in order to maintain wall thickness by restrictingelongation to approximately 2%. The expanded OD was, again, 154 mm withthe average wall thickness measured at 6.71 mm. The Q&T material wasexpanded in the same way and produced an average wall thickness of 6.79mm.

[0030] For the rotary-expanded VM42, the expansion demands comprised anaxial force of approximately 20000 lbf, generating a torque of 2750ftlbs at a tool pressure of around 1400 psi.

[0031] Post-Expansion Tensile Properties

[0032] The post-expansion longitudinal tensile properties were evaluatedon all three specimens in accordance with BS EN 10002 Pt 1: 2001. Theresults are listed below. Cone Rotary Rotary Expanded Expanded ExpandedVM42 VM42 Q&T Ultimate Tensile Stress 505 565 621 73.2 82.0 90.1 0.2%Offset Proof Stress 485 521 570 70.3 75.6 82.7 Elongation 22.7 18.3 14.8Cross Sectional Area 90.16 81.31 85.57 Gauge Length mm 50 50 50

[0033] Collapse Testing

[0034] The collapse samples were 1430 mm, or greater, in length, givinga sample length in excess of 9.2 times the OD. The collapse test wasconducted in a sealed vessel at a ramp rate of between 6 and 9psi/second, with the pressure continually recorded during the test. Thecollapse pressure was determined by the sudden pressure drop, resultingfrom the instantaneous sample volume change on collapse.

[0035] The collapse pressures are tabulated below. Cone Rotary ConeRotary Expanded Expanded Expand d Expanded VM42 VM42 VM42¹ Q&T Length9.29 ˜10 >8 9.29 OD OD OD OD D/t 21.12 22.93 21.4 22.78 API 5C3 Collaps4119 3405 4012 3663 Pressure Estimate, psi Actual Collapse 3232 38303147 4127 Pressure, psi Difference from −21.5% +12.5% −21.6% +12.7%Estimate

[0036] Discussion

[0037] The tests demonstrate that the collapse resistance of compliantrotary expanded tubulars is superior to equivalent tubulars expandedusing a cone-swaging method. The collapse pressure obtained for thecone-expanded sample used in these tests was consistent with publishedresults (P. Sutter et al, “Developments of Grades for SeamlessExpandable Tubes”, Corrosion 2001, Paper no. 021, Houston Tex., NACEInternational, 2001). Furthermore, whilst the cone-expanded sampleexhibited a collapse pressure over twenty percent lower than the APIprediction, the two different rotary expanded materials exceeded the APIestimate by 12.5%.

[0038] The applicant, although not wishing to be bound by theory,attributes the difference in collapse performance between rotary andcone-expanded tubulars to the orientation of dislocation arrays producedby the differing cold working process, that is the strain path ishelical in the rotary process as opposed to radial in the cone method.This means that on loading in a collapse mode, the dislocationsubstructure for helically-expanded material is not aligned in a way tosuffer from the Bauschinger effect, which relies on total or partialreversed loading. An alternative/contributory factor in rotary-expandedcollapse performance is the localised concentration of compressive coldwork in the bore of the tubular.

[0039] Additionally, for casing-compliant expansions, the collapseresistance in annular and full-system collapse tests have developedresistance far greater than would be anticipated from consideration ofthe individual tubular capabilities. It is believed this is due to thecasing resisting the geometry changes necessary for collapse of theinternal tubular.

[0040] Published data on cone-expanded tubulars demonstrates that astrain-ageing process can recover collapse resistance, presumably byrestricting the mobility of dislocations generated by cold work ratherthan from the increase in the yield strength of the material. However,strain-ageing is a diffusion-related process and, as such, is dependenton exposure of the material to an elevated temperature for a period oftime. As the necessary duration is kinetically related to the exposuretemperature, this process is dependent on well-temperature.

[0041] An ageing treatment of 5 hrs at 175° C. is quoted. (R. Mack & AFilippov, “The Effects of Cold Work and Strain Aging on the Hardness ofSelected Grades of OCTG and on the SSC Resistance Of API P-110—Resultsof Laboratory Experiments”, Corrosion 2002, Paper no. 066, Denver Colo.,NACE International, 2002) as a realistic simulation for expanded P-110material based on a kinetics study. The suppliers have suggested 30 minsat 250° C. for VM42 material. It is assumed that this study consisted ofa series of heat treatments of varying time and temperature to deriveactivation energies and rate constants as per standard Arrheniusrelationships, i.e. by plotting In(k) vs 1/T to find the gradient andintercept for k=k_(o)exp(−E_(A)/RT). The “reaction” in this case is thestrain-ageing treatment to produce peak hardness or “full-pinning”.

[0042] The cone-expanded VM42 material was tested after more than eightmonths exposure to ambient temperatures and did not show even a partialrecovery of collapse strength when compared to published data (P. Sutteret al).

[0043] Finally, following strain-ageing, a rotary-expanded carbon or lowalloy steel tubular could be expected to increase in collapse strength,from its existing high level, by a small extent due to an increase inyield strength.

[0044] It will be apparent to those of skill in the art that theabove-described embodiment is merely exemplary of the present inventionand that various modifications and improvements may be made thereto,without departing from the present invention. For example, in otherembodiments of the invention, the radial forces imparted by the rollers18 as described above may be achieved by other means, for example by useof a tool which is advanced axially without rotation, and which featuresa plurality of rollers which are rotatable about an axis perpendicularto the tool longitudinal axis, such as the ACE (Trade Mark) toolsupplied by the applicant.

[0045] In other embodiments, bearing members other than rollers, such asballs or indeed non-rotating members may be utilised to provide therequired axial force, although use of non-rotating members wouldincrease the tool-to-tubular friction and increase the forces necessaryto move the tool through the tubular.

1. A method of increasing the collapse resistance of a tubular, themethod comprising: (a) locating a tool having at least one bearingmember within a tubular; (b) placing the bearing member in engagementwith a wall of the tubular to apply a radial force to a discrete zone ofthe wall; and (c) applying said radial force to further discrete zonesof the wall, whereby the level of radial force is selected such that thecollapse resistance of the tubular increases.
 2. The method of claim 1,wherein said radial force is selected to induce compressive yield of atleast an inner portion of the wall.
 3. The method of claim 1, whereinsaid radial force is selected to induce plastic deformation of at leastan inner portion of the wall.
 4. The method of claim 1, wherein thebearing member is a rolling element and the tool is moved relative tothe tubular to provide a rolling contact between the rolling element andthe tubular wall.
 5. The method of claim 1, further comprising movingthe tool relative to the tubular to provide a sliding contact betweenthe bearing member and the tubular wall.
 6. The method of claim 1,wherein the tool is advanced axially relative to the tubular.
 7. Themethod of claim 1, wherein the tool is rotated relative to the tubularabout a longitudinal axis of the tubular.
 8. The method of claim 1,wherein the tool is located within the tubular.
 9. The method of claim1, wherein the tubular is subject to a degree of diametric expansion.10. The method of claim 9, wherein the tubing is subject to permanentdiametric expansion.
 11. The method of claim 1, wherein the tubularexperiences little or no diametric expansion.
 12. The method of claim 1,wherein the tool is moved relative to the tubular such that the bearingmember describes a helical path along the tubular wall.
 13. The methodof claim 1, wherein the tool has a plurality of bearing members, andeach bearing member is urged into engagement with the wall of thetubular to impart a radial force to a respective discrete zone of thetubular wall.
 14. The method of claim 13, wherein the respectivediscrete zones are circumferentially spaced.
 15. The method of claim 13,wherein the respective discrete zones are axially spaced.
 16. The methodof claim 1, wherein the bearing member applies the radial force to thetubular wall as a point load.
 17. The method of claim 1, wherein thebearing member applies the radial force to the tubular wall as a lineload.
 18. The method of claim 1, wherein the bearing member is appliedpressure actuated.
 19. The method of claim 1, wherein the tool comprisesa plurality of bearing members and at least one of the bearing membersis independently radially movable.
 20. The method of claim 1, whereinthe tool comprises a ball-peening tool and is impacted against the innersurface of the wall.
 21. The method of claim 1, wherein the tubular hasbeen previously swage-expanded.
 22. The method of claim 1, furthercomprising swage-expanding the tubular prior to steps (b) and (c). 23.The method of claim 1, when executed on surface.
 24. The method of claim1, when executed downhole.
 25. The method of claim 1, wherein thetubular is located within a larger diameter tubular.
 26. The method ofclaim 25, wherein the larger diameter tubular is substantiallyunexpandable.
 27. The method of claim 1, wherein the tool creates astrain path in the wall of the tubular having a circumferential element.28. The method of claim 27, wherein the tool creates a circumferentialstrain path.
 29. The method of claim 1, wherein the tool creates ahelical strain path.
 30. A method of increasing the collapse resistanceof a tubular, the method comprising diametrically expanding the tubularwithin a larger diameter tubular.
 31. A method of increasing thecollapse resistance of a tubular, the method comprising applying radialforces to discrete areas of a tubular wall.
 32. The method of claim 31,comprising applying said radial force using a mechanical tool.
 33. Themethod of claim 32, wherein the tool creates a strain path in the wallof the tubular having a circumferential element.
 34. The method of claim33, wherein the tool creates a circumferential strain path.
 35. Themethod of claim 32, wherein the tool creates a helical strain path. 36.A tubular as treated by claim
 31. 37. A method of increasing thecollapse resistance of a tubular, the method comprising increasing atleast one of the strength and hardness of at least the inner bore wall.38. The method of claim 37, comprising increasing at least one of thestrength and hardness of at least the inner bore wall by strainhardening.
 39. The method of claim 37, comprising increasing at leastone of the strength and hardness of at least the inner bore wall by coldwork.
 40. The method of claim 37, comprising increasing at least one ofthe strength and hardness of at least the inner bore wall bymetallurgical transformation.
 41. The method of claim 37, comprisingincreasing at least one of the strength and hardness of at least theinner bore wall by diffusion of elements, which elements promoteincreased hardness.
 42. A metallic tubular having an inner bore wall ofrelatively high strength and hardness.
 43. A method of increasing acollapse resitance of a tubular comprising: locating a tubular inwellbore, the tubular having an inner surface; and inducing acompressive stress in the inner suface thereby increasing the collapseresistance of the tubular.
 44. The method of claim 43, wherein thecompressive stress is induced in the inner surface of the tubular priorto locating the tubular in the wellbore.
 45. The method of claim 43,wherein inducing a compressive stress in the inner surface comprisesnitriding.
 46. The method of claim 43, wherein inducing a compressivestress in the inner surface comprises: placing a stress induction memberproximate a portion of the inner surface of the tubular; and imparting aradial stress to the inner surface of the tubular via the stressinduction member.
 47. The method of claim 46, wherein the stressinduction member comprises a rotary expansion tool.
 48. The method ofclaim 47, wherein inducing a compressive stress in the inner surfacecomprises imparting a radial stress to the inner surface of the tubularvia the stress induction member.
 49. The method of claim 48, furthercomprising monitoring one or more parameters while imparting the radialstress to the inner surface of the tubular via the stress inductionmember.
 50. The method of claim 49, wherein monitoring one or moreparameters comprises monitoring the one or more parameters with one ormore fiber optic sensors.
 51. The method of claim 50, wherein monitoringthe one or more parameters with one or more fiber optic sensorscomprises monitoring one or more fiber optic sensors distributed atdifferent discrete zones along the tubular.
 52. The method of claim 49,wherein monitoring the one or more parameters comprises monitoring atleast one of the radial force imparted to the inner surface of thetubular and an outer diameter of the tubular.
 53. The method of claim49, further comprising: applying a fluid pressure to the stressinduction member in order to impart the radial force on the innersurface of the tubular; and varying the fluid pressure applied to thestress induction member in response to one or more of the monitoredparameters.